Four p38 MAPK isoforms (alpha, beta, gamma and delta respectively), have been identified each displaying different patterns of tissue expression in man. The p38 MAPK alpha and beta isoforms are found ubiquitously in the body, being present in many different cell types. The alpha isoform is well characterized in terms of its role in inflammation. Although studies using a chemical genetic approach in mice indicate that the p38 MAPK beta isoform does not play a role in inflammation (O'Keefe, S. J. et al., J. Biol. Chem., 2007, 282(48), 34663-71), it may be involved in pain mechanisms through the regulation of COX2 expression (Fitzsimmons, B. L. et al., Neuroreport, 2010, 21(4), 313-7). These isoforms are inhibited by a number of previously described small molecular weight compounds. Early classes of inhibitors were highly toxic due to the broad tissue distribution of these isoforms which resulted in multiple off-target effects of the compounds. Furthermore, development of a substantial number of inhibitors has been discontinued due to unacceptable safety profiles in clinical studies (Pettus, L. H. and Wurz, R. P., Curr. Top. Med. Chem., 2008, 8(16), 1452-67). As these adverse effects vary with chemotype, and the compounds have distinct kinase selectivity patterns, the observed toxicities may be structure-related rather than p38 mechanism-based. More recently, compounds with greater potency and specificity for p38α/β MAPK have been developed; however, levels of efficacy achieved in the treatment of chronic inflammatory diseases, including rheumatoid arthritis (SCIO-469, Genovese et al., J. Rheumatol., 2011, 38, 846-54; Pamapimod, Cohen et al., Arthritis Rheum., 2009, 60, 335-344; BMS-582949, Schieven et al., Arthritis Rheum., 2010, 62, Suppl. 10:1513) and COPD (Losmapimod, Watz et al., Lancet Resp. Med., 2014, 2, 63-72) have been disappointing. Furthermore, it is noteworthy that a p38 MAPK inhibitor was found to deliver benefit for patients with IBD after one week's treatment which was not sustained over a four week course of treatment (BIRB-796, Schreiber, S. et al., Clin. Gastro. Hepatology, 2006, 4, 325-334).
An important conclusion drawn from these studies is that use of a target specific kinase inhibitor may not be sufficient to achieve and sustain therapeutic benefit in complex inflammatory diseases, where dysregulation of multiple immuno-inflammatory pathways and biological adaption can by-pass blockade of a single target mechanism, resulting in the loss of response. It can be argued that for complex inflammatory disease such as COPD, rheumatoid arthritis and IBD, inhibitors that target a set of kinases that are critical for regulation of the different immuno-inflammatory mechanisms linked to pathology will have greater potential to achieve efficacy and a sustained therapeutic response.
The role of p38 MAPK-alpha in the regulation of inflammatory pathways has been investigated extensively and is well established. Less is known about the p38 MAPK gamma and delta isoforms, which, unlike the alpha and beta isozymes are expressed in specific tissues and cells. The p38 MAPK-delta isoform is expressed more highly in the pancreas, testes, lung, small intestine and the kidney. It is also abundant in macrophages and detectable in neutrophils, CD4+ T cells and in endothelial cells (Shmueli, O. et al., Comptes Rendus Biologies, 2003, 326(10-11), 1067-1072; Smith, S. J. Br. J. Pharmacol., 2006, 149, 393-404; Hale, K. K., J. Immunol., 1999, 162(7), 4246-52; Wang, X. S. et al., J. Biol. Chem., 1997, 272(38), 23668-23674). Very little is known about the distribution of p38 MAPK gamma although it is expressed more highly in brain, skeletal muscle and heart, as well as in lymphocytes and macrophages (Shmueli, O. et al., Comptes Rendus Biologies, 2003, 326(10-11), 1067-1072; Hale, K. K., J. Immunol., 1999, 162(7), 4246-52; Court, N. W. et al., J. Mol. Cell. Cardiol., 2002, 34(4), 413-26; Mertens, S. et al., FEBS Lett., 1996, 383(3), 273-6). Evidence that the p38 MAPK-gamma and p38 MAPK-delta kinases are expressed in immunologically important and pro-inflammatory cell types has raised interest in their functions relative to p38 MAPK-alpha. Selective small molecule inhibitors of p38 MAPK gamma and p38 MAPK delta are not currently available to assess the roles of these kinases pharmacologically, although one previously disclosed compound, BIRB 796, is known to possess pan-isoform inhibitory activity. The inhibition of p38 MAPK gamma and delta isoforms is observed at higher concentrations of the compound than those required to inhibit p38 MAPK alpha and p38 beta (Kuma, Y., J. Biol. Chem., 2005, 280, 19472-19479). In addition BIRB 796 also impaired the phosphorylation of p38 MAPKs or JNKs by the upstream kinase MKK6 or MKK4. Kuma discussed the possibility that the conformational change caused by the binding of the inhibitor to the MAPK protein may affect the structure of both its phosphorylation site and the docking site for the upstream activator, thereby impairing the phosphorylation of p38 MAPKs or JNKs.
p38 MAP kinase is believed to play a pivotal role in many of the signalling pathways that are involved in initiating and maintaining chronic, persistent inflammation in human disease, for example, in severe asthma and in COPD (Chung, F., Chest, 2011, 139(6), 1470-1479). There is now an abundant literature which demonstrates that p38 MAP kinase is activated by a range of pro-inflammatory cytokines and that its activation results in the recruitment and release of additional pro-inflammatory cytokines. For instance Smith describes the inhibitory effect of p38 MAP kinase inhibitors on TNFα release from human PBMCs. However, the production of some cytokines (IL-8 and GM-CSF) by lung tissue macrophages isolated from smokers and ex-smokers was relatively insensitive to p38α/β MAPK inhibitors and Smith suggests that the abundance of p38 MAPK-delta expressed in these cells might account for the diminished effects of the compounds (Smith et al., Br. J. Pharmacol., 2006, 149, 393-404). Risco et al., (Proc. Natl. Acad. Sci. U.S.A., 2012, 109, 11200-11205) have used p38 MAPK-gamma and p38 MAPK-delta gene knockout mice to investigate the roles of these p38 isoforms in pathways regulating cytokine production by macrophages. These studies established that in mice both kinases are essential for innate immune inflammatory responses including proinflammatory cytokine production. More recently, Criado, G. et al., (Arthritis Rheum., 2014, 66(5), 1208-17) have demonstrated that in a mouse model of inflammatory arthritis reduced disease severity in p38γ/δ−/− mice was associated with lower cytokine production and immunological activation than in normal control mice, indicating that p38 MAPK gamma and p38 MAPK delta are crucial regulators of inflammatory joint pathology. These findings suggest that in addition to p38 MAPK alpha, p38 MAPK gamma and p38 MAPK delta are potential therapeutic targets in complex diseases that involve innate and adaptive immune responses such as COPD.
The use of inhibitors of p38 MAP kinase in the treatment of chronic obstructive pulmonary disease (COPD) has also been investigated. Small molecule inhibitors targeted to p38 MAPK a/8 have proved to be effective in reducing various parameters of inflammation in cells and in tissues obtained from patients with COPD, who are generally corticosteroid insensitive, (Smith, S. J., Br. J. Pharmacol., 2006, 149, 393-404) as well as in various in vivo animal models (Underwood, D. C. et al., Am. J. Physiol., 2000, 279, L895-902; Nath, P. et al., Eur. J. Pharmacol., 2006, 544, 160-167). Irusen and colleagues have also suggested the possible involvement of p38 MAPK α/β with corticosteroid insensitivity via the reduction of binding affinity of the glucocorticoid receptor (GR) in nuclei (Irusen, E. et al., J. Allergy Clin. Immunol., 2002, 109, 649-657). Clinical experience with a range of p38 MAP kinase inhibitors, including AMG548, BIRB 796, VX702, SCIO469 and SCIO323 has been described (Lee, M. R. and Dominguez, C., Current Med. Chem., 2005, 12, 2979-2994).
COPD is a condition in which the underlying inflammation is reported to be substantially resistant to the anti-inflammatory effects of inhaled corticosteroids. Consequently, a superior strategy for treating COPD would be to develop an intervention which has both inherent anti-inflammatory effects and the ability to increase the sensitivity of the lung tissues of COPD patients to inhaled corticosteroids. A recent publication of Mercado (Mercado, N., et al., Mol. Pharmacol., 2011, 80(6), 1128-1135) demonstrates that silencing p38 MAPK-γ has the potential to restore sensitivity to corticosteroids. P38 MAPK alpha (Mercado, N. et al., PLoS ONE, 2012, 7(7), e41582, 1-9) and JNK (Papi et al., J. Allergy Clin. Immunol., 2013, 132, 1075-1085) have also been reported to have roles in regulating corticosteroid insensitivity and Armstrong et al. (JPET, 2011, 338, 732-740) have shown that the mixed p38 isoform inhibitor BIRB-796 and the corticosteroid dexamethasone have synergistic anti-inflammatory effects on COPD alveolar macrophages. Consequently there may be a benefit for patients in the use of a less p38 alpha-specific MAP kinase inhibitor for the treatment of COPD and severe asthma.
Many patients diagnosed with asthma or with COPD continue to suffer from uncontrolled symptoms and from exacerbations of their medical condition that can result in hospitalisation. This occurs despite the use of the most advanced, currently available treatment regimens, comprising of combination products of an inhaled corticosteroid and a long acting β-agonist. Data accumulated over the last decade indicates that a failure to manage effectively the underlying inflammatory component of the disease in the lung is the most likely reason that exacerbations occur. Given the established efficacy of corticosteroids as anti-inflammatory agents and, in particular, of inhaled corticosteroids in the treatment of asthma, these findings have provoked intense investigation. Resulting studies have identified that some environmental insults invoke corticosteroid-insensitive inflammatory changes in patients' lungs. An example is the response arising from virally-mediated upper respiratory tract infections (URTI), which have particular significance in increasing morbidity associated with asthma and COPD.
Epidemiological investigations have revealed a strong association between viral infections of the upper respiratory tract and a substantial percentage of the exacerbations suffered by patients already diagnosed with chronic respiratory diseases. Some of the most compelling data in this regard derives from longitudinal studies of children suffering from asthma (Papadopoulos, N. G. et al., Paediatr. Respir. Rev., 2004, 5(3), 255-260). A variety of additional studies support the conclusion that a viral infection can precipitate exacerbations and increase disease severity. For example, experimental clinical infections with rhinovirus have been reported to cause bronchial hyper-responsiveness to histamine in asthmatics that is unresponsive to treatment with corticosteroids (Grunberg, K., et al., Am. J. Respir. Crit. Care Med., 2001, 164(10), 1816-1822). Further evidence derives from the association observed between disease exacerbations in patients with cystic fibrosis and HRV infections (Wat, D. et al., J. Cyst. Fibros., 2008, 7, 320-328). Also consistent with this body of data is the finding that respiratory viral infections, including rhinovirus, represent an independent risk factor that correlates negatively with the 12 month survival rate in paediatric, lung transplant recipients (Liu, M. et al., Transpl. Infect. Dis., 2009, 11(4), 304-312).
TLR3 is an endosomal pathogen pattern recognition receptor that senses viral dsRNA that is produced during viral infection. In human bronchial epithelial cells (BEAS2B) the TLR3 pathway is activated in response to rhinovirus infection (RV1B and RV39) (Wang et al., J. Immunol., 2009, 183, 6989-6997). Inhaled dsRNA and rhinovirus infection evoke neutrophilic exacerbation in allergic mice with established experimental asthma (Mahmutovic-Persson et al., Allergy, 2014, 69(3), 348-358). In an allergic asthma model, rhinovirus-infected TLR3 knockout mice demonstrated reduced infiltration of neutrophils and macrophages into the lungs and significantly lower airways inflammation when compared with TLR3 positive controls (Wang, Q. et al., PLoS Pathog., 7(5), e1002070). Taken together these observations suggest that activation of the TLR3-pathway is likely to play an important role in the development of airways inflammation and exacerbations of respiratory disease in response to rhinovirus-mediated respiratory tract infections
In human rhinovirus infected cells the activation of TLR3 has been shown to involve the receptor-recruitment and activation of c-Src kinase which mediates multiple downstream cellular effects. A small number of studies have appeared that link the activation of cellular Src (Src1 or p60-Src) or Src family kinases to specific responses following infection with viruses. These include a report that adenovirus elicits a PI3 kinase mediated activation of Akt through a c-Src dependent mechanism. Syk kinase activity is reported to be controlled by c-Src as an upstream kinase in HRV infection (Lau et al., J. Immunol., 2008, 180, 870-880). It has also been suggested that Rhinovirus-39 induced IL-8 production in epithelial cells depends upon Src kinase activation (Bentley, J. K. et al., J. Virol., 2007, 81, 1186-1194). Finally, it has been proposed that activation of Src kinase is involved in the induction of mucin production by rhinovirus-14 in epithelial cells and sub-mucosal glands (Inoue, D. et al., Respir. Physiol. Neurobiol., 2006, 154(3), 484-499).
It has been disclosed previously that compounds that inhibit p59-HCK are effective against influenza virus replication (Charron, C. E. et al., WO 2011/070369). Certain p38 MAPK inhibitors have also been described as inhibitors of the replication of respiratory syncitial virus (Cass, L. et al., WO 2011/158039).
For the reasons summarised above, compounds designed to treat chronic respiratory diseases that combine inhibition of c-Src and p59-HCK kinases with the inhibition of p38 MAPKs, are expected to be particularly efficacious.
In addition to playing key roles in cell signalling events which control the activity of pro-inflammatory pathways, kinase enzymes are now also recognised to regulate the activity of a range of cellular functions. Among those which have been discussed recently are the maintenance of DNA integrity (Shilo, Y. Nat. Rev. Cancer, 2003, 3, 155-168) and co-ordination of the complex processes of cell division. An illustration of recent findings is a publication describing the impact of a set of inhibitors acting upon the so-called “Olaharsky kinases” on the frequency of micronucleus formation in vitro (Olaharsky, A. J. et al., PLoS Comput. Biol., 2009, 5(7), e1000446). Micronucleus formation is implicated in, or associated with, disruption of mitotic processes and is therefore an undesirable manifestation of potential toxicity. Inhibition of glycogen synthase kinase 3α (GSK3α) was found to be a particularly significant factor that increases the likelihood of a kinase inhibitor promoting micronucleus formation. Recently, inhibition of the kinase GSK3β with RNAi was also reported to promote micronucleus formation (Tighe, A. et al., BMC Cell Biology, 2007, 8:34).
It may be possible to attenuate the adverse effects arising from drug interactions with Olaharsky kinases, such as GSK3α, by optimisation of the dose and/or by changing the route of administration. However, it would be more advantageous to identify therapeutically useful molecules that demonstrate low or undetectable activity against these off-target enzymes and consequently elicit little or no disruption of mitotic processes, as measured in mitosis assays.
It is evident from consideration of the literature cited hereinabove that there remains a need to identify and develop new p38 MAP kinase inhibitors that have improved therapeutic potential over currently available treatments. Desirable compounds are those that exhibit a superior therapeutic index by exerting, at the least, an equally efficacious effect as previous agents but, in one or more respects, are less toxic at the relevant therapeutic dose. An objective of the present invention therefore, is to provide such a novel compound that inhibits the enzyme activity of p38 MAP kinase, for example with certain sub-type specificities (particularly alpha and gamma), as well as inhibiting the enzyme activity of tyrosine kinases within the Src family (such as p59-HCK and particularly c-Src) thereby possessing good anti-inflammatory properties, and suitable for use in therapy. The compound of the invention exhibits weak or no inhibitory activity of Olaharsky kinases, such as GSK3α and exhibits weak or no inhibitory activity of SYK kinase which contributes to its expected favourable safety profile.